As optical disks for recording and reproduction of music information including speech or video information and reproduction apparatus, a CD (Compact Disk) and an LD (Laser Disk) are well known.
A CD is an optical disk having a diameter of 12 cm, in which music information is digitally recorded using a coding technique called "linear PCM", and it has been used as an application recording medium for music. An LD is an optical disk having a diameter of 30 cm, in which video information with audio is recorded as analog signals, and it has been used as an application recording medium for video like a movie.
In recent years, in order to secure long-time recording and sufficient quality, there has been proposed an optical disk of about 12 cm in diameter, in which one or both of music information including speech and video information is/are digitally compressed and recorded with efficiency and, furthermore, having a file structure which facilitates data exchange with computers or communications.
FIGS. 5(a) to 5(c) are diagrams schematically illustrating the standard of a format when MPEG (Motion Picture Expert Group) data are recorded in a DVD (Digital Video Disk) which has been examined for practical use under the circumstances described above. In this format, data are recorded in units of packets as shown in FIG. 5(c), and some of the packets are managed together using information called a pack header.
Further, each of the packets is composed of information called a packet header which indicates the attribute of the packet, and data composed of plural frames. In the packet header, identification information such as "videoe" or "audio", control information, etc. are recorded.
When the medium (DVD) in which data are recorded as described above is reproduced using a reproduction apparatus, the reproduction apparatus is constructed so that an optical head irradiates the disk with a light beam and reads the recorded data as a change in reflectance of a light spot.
A description is given of a method for storing data in the medium having the structure described above.
As shown in FIG. 5(b), each pack comprises a plurality of packets, and generally the same contents (e.g., video data or audio data) are assigned to each packet. Now, the case of audio using a coding method called MPEG is considered. As shown in FIG. 5(b), when two packs which are adjacent each other with respect to the same contents (in this case, audio using the MPEG coding) are extracted, there arises a case where one packet is recorded over the two packs. In this case, it is necessary to divide the packet into two packets and insert a pack header or a packet header between the two packets, and this results in complicated authoring. Further, when retrieval or jumping has been carried out, data cannot be always reproduced from the beginning of the pack.
As shown in FIG. 5(a), when the packs are recorded by one-to-one correspondence with sectors which are physical units for data management in the recording medium and include address information at their beginnings, access is facilitated in an application such as a DVD. However, this feature cannot be satisfactorily utilized because of the above-described problem.
As described above, in the conventional optical disk, there arises a case where data of one packet to be recorded is stored over adjacent two packs. On the other hand, with respect to such a multimedia optical disk, the following demands are made: to retrieve object audio information or video information as quickly and easily as possible; to secure synchronization between audio information and video information relating to the audio information; and to facilitate authoring when data above is interleaved on one track of the optical disk using the pack and packet structure.
In the optical disk having the above-described data structure, however, the following process steps are required for data reproduction: searching for a packet header for identifying frames, analyzing the information described in the packet header, searching for a frame synchronization signal (hereinafter referred to as a frame sync signal), and detecting it. These process steps make the speedy data search and simple authoring difficult. Further, when the reproduction apparatus is not provided with a data decoding function, it is general that data are output to the digital interface in frame units for decoding in an external decoder (e.g., IEC958 standard). In this case, each frame is output by detecting a frame sync signal which corresponds to the deepest layer in the hierarchical structure, and this causes the burden to the hardware.